For me, I don't think there is a specified time to buy, and when not to buy. If we play by the rules of trading, which is Buy low and sell high, then there is not specific time to buy or sell.
Coins to invest are all out there, but the right one to invest is the question. For me, I invested in EOS, ETH, LTC NAS. These are some good coins, and I have made a little profit from them. This investment was done when the market was on the downtrend. There are still chances on going in......another one is GRIN and BOMB..........